Microreplicated article

ABSTRACT

A microreplicated article is disclosed. The article includes a web including first and second opposed surfaces. The first surface includes a first microreplicated structure having a plurality of first features. The second surface includes a second microreplicated structure having a plurality of second features. Corresponding opposed features cooperate to form a lens features.

FIELD

The disclosure relates generally to the continuous casting of materialonto a web, and more specifically to the casting of articles having ahigh degree of registration between the patterns cast on opposite sidesof the web.

BACKGROUND

In the fabrication of many articles, from the printing of newspapers tothe fabrication of sophisticated electronic and optical devices, it isnecessary to apply some material that is at least temporarily in liquidform to opposite sides of a substrate. It is often the case that thematerial applied to the substrate is applied in a predetermined pattern;in the case of e.g. printing, ink is applied in the pattern of lettersand pictures. It is common in such cases for there to be at least aminimum requirement for registration between the patterns on oppositesides of the substrate.

When the substrate is a discrete article such as a circuit board, theapplicators of a pattern may usually rely on an edge to assist inachieving registration. But when the substrate is a web and it is notpossible to rely on an edge of the substrate to periodically refer to inmaintaining registration, the problem becomes a bit more difficult.Still, even in the case of webs, when the requirement for registrationis not severe, e.g. a drift out of perfect registration of greater than100 microns is tolerable, mechanical expedients are known forcontrolling the material application to that extent. The printing art isreplete with devices capable of meeting such a standard.

However, in some products having patterns on opposite sides of asubstrate, a much more accurate registration between the patterns isrequired. In such a case, if the web is not in continuous motion,apparatuses are known that can apply material to such a standard. And ifthe web is in continuous motion, if it is tolerable, as in e.g. sometypes of flexible circuitry, to reset the patterning rolls to within 100microns, or even 5 microns, of perfect registration once per revolutionof the patterning rolls, the art still gives guidelines about how toproceed.

However, in e.g. optical articles such as brightness enhancement films,it is required for the patterns in the optically transparent polymerapplied to opposite sides of a substrate to be out of registration by nomore than a very small tolerance at any point in the tool rotation. Thusfar, the art is silent about how to cast a patterned surface on oppositesides of a web that is in continuous motion so that the patterns arekept continuously, rather than intermittently, in registration within100 microns.

SUMMARY

One aspect of the present disclosure is directed to a microreplicatedarticle. The microreplicated article includes a flexible substratehaving first and second opposed surfaces, a first coated microreplicatedpattern on the first surface, and a second coated microreplicatedpattern on the second surface. First and second microreplicated patternsare registered to better than about 100 microns, and preferably areregistered to within about 75 microns, and more preferably to withinabout 50 microns, and most preferably to within about 10 microns. Inanother embodiment, the first and second patterns cooperate to form aplurality of lenticular lenses.

Another aspect of the present disclosure is directed to a method ofmaking a microreplicated lens. The method includes providing asubstrate, in web form, having first and second opposed surfaces andpassing the substrate through a casting apparatus to form a plurality oflens features. The lens features are comprised of a firstmicroreplicated patterned structure on the first surface and a secondmicroreplicated patterned structure on the second surface.

Definitions

In the context of this disclosure, “registration,” means the positioningof structures in a set location in relation to the edge of a web and toother structures on the opposite side of the same web.

In the context of this disclosure, “web” means a sheet of materialhaving a fixed dimension in one direction and either a predetermined orindeterminate length in the orthogonal direction.

In the context of this disclosure, “continuous registration,” means thatat all times during rotation of first and second patterned rolls thedegree of registration between structures on the rolls is better than aspecified limit.

In the context of this disclosure, “microreplicated” or“microreplication” means the production of a microstructured surfacethrough a process where the structured surface features retain anindividual feature fidelity during manufacture, from product-to-product,that varies no more than about 100 micrometers.

BRIEF DESCRIPTION OF THE DRAWING

In the several figures of the attached drawing, like parts bear likereference numerals, and:

FIG. 1 illustrates a perspective view of an example embodiment of asystem including a system according to the present disclosure;

FIG. 2 illustrates a close-up view of a portion of the system of FIG. 1according to the present disclosure;

FIG. 3 illustrates another perspective view of the system of FIG. 1according to the present disclosure;

FIG. 4 illustrates a schematic view of a an example embodiment of acasting apparatus according to the present disclosure;

FIG. 5 illustrates a close-up view of a section of the casting apparatusof FIG. 4 according to the present disclosure;

FIG. 6 illustrates a schematic view of an example embodiment of a rollmounting arrangement according to the present disclosure;

FIG. 7 illustrates a schematic view of an example embodiment of amounting arrangement for a pair of patterned rolls according to thepresent disclosure;

FIG. 8 illustrates a schematic view of an example embodiment of a motorand roll arrangement according to the present disclosure;

FIG. 9 illustrates a schematic view of an example embodiment of a meansfor controlling the registration between rolls according to the presentdisclosure;

FIG. 10 illustrates a schematic view of an example embodiment of a rollcontrolling arrangement according to the present disclosure;

FIG. 11 illustrates a block diagram of an example embodiment of a methodand apparatus for controlling registration according to the presentdisclosure;

FIG. 12 illustrates a cross-sectional view of an article made accordingto the present disclosure.

DETAILED DESCRIPTION

Generally, the invention of the present disclosure is directed to aflexible substrate coated with microreplicated patterned structures oneach side. The microreplicated articles are registered with respect toone another to a high degree of precision. Preferably, the structures onopposing sides cooperate to give the article optical qualities asdesired, and more preferably, the structures are a plurality of lensfeatures.

EXAMPLE #1 Microreplicated Article

Referring to FIG. 12, illustrated is an example embodiment of atwo-sided microreplicated article 1200. The article 1200 includes a web1210 substrate having opposed first and second surfaces 1220, 1230.First and second surfaces 1220, 1230 include first and secondmicroreplicated structures 1225, 1235, respectively. Firstmicroreplicated structure 1225 includes a plurality of arcuate features1226, which in the embodiment shown are cylindrical lenses with aneffective diameter of about 142 microns. Second microreplicatedstructure 1235 includes a plurality of saw-tooth or pyramidal prismaticfeatures 1236.

In the example embodiment shown, first and second features 1226, 1236have the same pitch or period of repetition P, e.g., the period of thefirst feature is about 150 microns, and the period of repetition of thesecond feature is the same. Typically, the ratio of the period of thefirst and second features is a whole number ratio (or the inverse),though other combinations are permissible. The features shown are ofindefinite length in a down-web direction.

In the example embodiment shown, opposed microreplicated features 1226,1236 cooperate to form a plurality of lens features 1240. In the exampleembodiment shown, the lens features 1240 are lenticular lenses. Sincethe performance of each lens feature 1240 is a function of the alignmentof the opposed features 1229, 1239 forming each lens, precisionalignment or registration of the lens features is preferable.

Optionally, the article 1200 also includes first and second land areas1227, 1237. The land area is defined as the material between thesubstrate surfaces 1220, 1230 and the bottom of each respective feature,i.e., valleys 1228, 1238. Typically, the first land area 1228 is atleast about 10 microns on the lens side and the second land area 1238 isabout at least about 25 microns on the prism side. The land area assistsin the features having good adherence to the web and also aid inreplication fidelity.

The article 1200 described above was made using an apparatus and methodfor producing precisely aligned microreplicated structures on opposedsurfaces of the web, the apparatus and methods which are described indetail below. The embodiment produced by Applicants was made using theusing a web made from polyethylene terephthalate (PET), 0.0049 inchesthick. Other web materials can be used, for example, polycarbonate.

The first microreplicated structure was made on a first patterned rollby casting and curing a curable liquid onto the first side of the web.The first curable liquid was a light sensitive acrylate resin solutionincluding photomer 6010, available from Cognis Corp., Cincinnati, Ohio;SR385 tetrahydrofurfuryl acrylate and SR238 (70/15/15%) 1,6-hexanedioldiacrylate, both available from Satomer Co., Expon, Pa.; Camphorquinone,available from Hanford Research Inc., Stratford, Conn.; andEthyl-4-dimethylamino Benzoate (0.75/0.5%), available from AldrichChemical Co., Milwaukee, Wis. The second microreplicated structure wasmade on a second patterned roll by casting and curing a curable liquidonto the second side of the web. The second curable liquid used was thesame as the first curable liquid.

After each respective structure was cast into a pattern, each respectivepattern was externally cured using a curing light source including anultraviolet light source. A peel roll was then used to remove themicroreplicated article from the second patterned roll. Optionally, arelease agent or coating can be used to assist removal of the patternedstructures from the patterned tools.

The process settings used to create the article described above are asfollows. A web speed of about 1.0 feet per minute with a web tensioninto and out of casting apparatus of about 2.0 pounds force were used. Apeel roll draw ratio of about 5% was used to pull the web off the secondpatterned tool. A nip pressure of about 4.0 pounds force was used. Thegap between the first and second patterned rolls was about 0.010 inches.Resin was supplied to the first surface of the web using a droppercoating apparatus and resin was supplied to the second surface at a rateof about 1.35 ml/min, using a syringe pump.

Curing the first microreplicated structure was accomplished with anOriel 200-500 W Mercury Arc Lamp at maximum power and a Fostec DCR II atmaximum power, with all the components mounted sequentially. Curing thesecond microreplicated structure was accomplished with a Spectral EnergyUV Light Source, a Fostec DCR II at maximum power, and an RSLI Inc.Light Pump 150 MHS, with all the components mounted sequentially.

The first patterned roll included a series of negative images forforming cylindrical lenses with a 142 micron diameter at 150 micronpitch. The second patterned roll included a series of negative imagesfor forming a plurality of symmetric prisms with 60 degree includedangle at 150 micron pitch.

Generally, the invention of the present disclosure can be made by asystem and method, disclosed hereinafter, for producing two-sidedmicroreplicated structures with side-to-side registration of better thanabout 100 microns, and preferably better than 50 microns, and morepreferably less than 25 microns, and most preferably less than 5microns. The system generally includes a first patterning assembly and asecond patterning assembly. Each respective assembly creates amicroreplicated pattern on a respective surface of a web having a firstand a second surface. A first pattern is created on the first side ofthe web and a second pattern is created on the second surface of theweb.

Each patterning assembly includes means for applying a coating, apatterning member, and a curing member. Typically, patterning assembliesinclude patterned rolls and a support structure for holding and drivingeach roll. Coating means of the first patterning assembly dispenses afirst curable coating material on a first surface of the web. Coatingmeans of the second patterning assembly dispenses a second curablecoating material on a second surface of the web, wherein the secondsurface is opposite the first surface. Typically, first and secondcoating materials are of the same composition.

After the first coating material is placed on the web, the web passesover a first patterned member, wherein a pattern is created in the firstcoating material. The first coating material is then cured or cooled toform the first pattern. Subsequently, after the second coating materialis placed on the web, the web passes over a second patterned member,wherein a pattern is created in the second coating material. The secondcoating material is then cured to form the second pattern. Typically,each patterned member is a microreplicated tool and each tool typicallyhas a dedicated curing member for curing the material. However, it ispossible to have a single curing member that cures both first and secondpatterned materials. Also, it is possible to place the coatings on thepatterned tools.

The system also includes means for rotating the first and secondpatterned rolls such that their patterns are transferred to oppositesides of the web while it is in continuous motion, and said patterns aremaintained in continuous registration on said opposite sides of the webto better than about 100 microns.

An advantage of the present invention is that a web having amicroreplicated structure on each opposing surface of the web can bemanufactured by having the microreplicated structure on each side of theweb continuously formed while keeping the microreplicated structures onthe opposing sides registered generally to within 100 microns of eachother, and typically within 50 microns, and more typically within 20microns, and most typically within 5 microns.

Referring now to FIGS. 1-2, an example embodiment of a system 110including casting apparatus 120 according to the present disclosure isillustrated. In the depicted casting apparatus 120, a web 122 isprovided to the casting apparatus 120 from a main unwind spool (notshown). The exact nature of web 122 can vary widely, depending on theproduct being produced. However, when the casting apparatus 120 is usedfor the fabrication of optical articles it is usually convenient for theweb 122 to be translucent or transparent, to allow curing through theweb 122. The web 122 is directed around various rollers 126 into thecasting apparatus 120.

Accurate tension control of the web 122 is required to achieve the bestresults the invention is capable of, so the web 122 is directed over atension-sensing device (not shown). In situations where it is desirableto use a liner web to protect the web 122, the liner web is typicallyseparated at the unwind spool and directed onto a liner web wind-upspool (not shown). The web 122 is typically directed via an idler rollto a dancer roller for precision tension control. Idler rollers directthe web 122 to a position between nip roller 154 and first coating head156.

In the depicted embodiment, first coating head 156 is a die coatinghead. However, other coating methods can be adapted to the apparatus, asone of ordinary skill in the art will appreciate. The web 122 thenpasses between the nip roll 154 and first patterned roll 160. The firstpatterned roll 160 has a patterned surface 162, and when the web 122passes between the nip roller 154 and the first patterned roll 160 thematerial dispensed onto the web 122 by the first coating head 156 isshaped into a negative of patterned surface 162.

While the web 122 is in contact with the first patterned roll 160,material is dispensed from second coating head 164 onto the othersurface of web 122. In parallel with the discussion above with respectto the first coating head 156, the second coating head 164 is also a diecoating arrangement including a second extruder (not shown) and a secondcoating die (not shown). In some embodiments, the material dispensed bythe first coating head 156 is a composition including a polymerprecursor and intended to be cured to solid polymer with the applicationof ultraviolet radiation.

Material that has been dispensed onto web 122 by the second coating head164 is then brought into contact with second patterned roll 174 with asecond patterned surface 176. In parallel with the discussion above, insome embodiments, the material dispensed by the second coating head 164is a composition including a polymer precursor and intended to be curedto solid polymer with the application of ultraviolet radiation.

At this point, the web 122 has had a pattern applied to both sides. Apeel roll 182 may be present to assist in removal of the web 122 fromsecond patterned roll 174. Typically, web tension into and out of thecasting apparatus is nearly constant.

The web 122 having a two-sided microreplicated pattern is then directedto a wind-up spool (not shown) via various idler rolls. If an interleavefilm is desired to protect web 122, it is typically provided from asecondary unwind spool (not shown) and the web and interleave film arewound together on the wind-up spool at an appropriate tension.

Referring to FIGS. 1-3, first and second patterned rolls are coupled tofirst and second motor assemblies 210, 220, respectively. Support forthe motor assemblies 210, 220 is accomplished by mounting assemblies toa frame 230, either directly or indirectly. The motor assemblies 210,220 are coupled to the frame using precision mounting arrangements. Inthe example embodiment shown, first motor assembly 210 is fixedlymounted to frame 230. Second motor assembly 220, which is placed intoposition when web 122 is threaded through the casting apparatus 120,needs to be positioned repeatedly and is therefore movable, both in thecross- and machine direction. Movable motor arrangement 220 ispreferably coupled to linear slides 222 to assist in repeated accuratepositioning, for example, when switching between patterns on the rolls.Second motor arrangement 220 also includes a second mounting arrangement225 on the backside of the frame 230 for positioning the secondpatterned roll 174 side-to-side relative to the first patterned roll160. Second mounting arrangement 225 preferably includes linear slides223 allowing accurate positioning in the cross machine directions.

Referring to FIG. 6, a motor mounting arrangement is illustrated. Amotor 633 for driving a tool or patterned roll 662 is mounted to themachine frame 650 and connected through a coupling 640 to a rotatingshaft 601 of the patterned roller 662. The motor 633 is coupled to aprimary encoder 630. A secondary encoder 651 is coupled to the tool toprovide precise angular registration control of the patterned roll 662.Primary 630 and secondary 651 encoders cooperate to provide control ofthe patterned roll 662 to keep it in registration with a secondpatterned roll, as will be described further hereinafter.

In the example embodiment shown, the tool roller 662 diameter istypically smaller than its motor 633 diameter. To accommodate thisarrangement, the two tool roller assemblies 610, 710 are installed asmirror images in order to be able to bring the two tool rollers 662, 762together as shown in FIG. 7. Referring also to FIG. 1, the first motorarrangement is typically fixedly attached to the frame and the secondmotor arrangement is positioned using movable optical quality linearslides. Reduction or elimination of shaft resonance is important as thisis a source of registration error allowing pattern position controlwithin the specified limits. Using a coupling 640 between the motor 633and shaft 650 that is larger than general sizing schedules specify willalso reduce shaft resonance caused by more flexible couplings. Bearingassemblies 660 are located in various locations to provide rotationalsupport for the motor arrangement.

Referring to FIG. 4, an example embodiment of a casting apparatus 420for producing a two-sided web 422 with registered microreplicatedstructures on opposing surfaces is illustrated. Assembly includes firstand second coating means 456, 464, a nip roller 454, and first andsecond patterned rolls 460, 474. Web 422 is presented to the firstcoating means 456, in this example a first extrusion die 456. First die456 dispenses a first curable liquid layer coating 470 onto the web 422.First coating 470 is pressed into the first patterned roller 460 bymeans of a nip roller 454, typically a rubber covered roller. While onthe first patterned roll 460, the coating is cured using an externalcuring source 480, for example, a lamp, of suitable wavelength light,typically an ultraviolet light.

A second curable liquid layer 481 is coated on the opposite side of theweb 422 using a second side extrusion die 464. The second layer 481 ispressed into the second patterned tool roller 474 and the curing processrepeated for the second coating layer 481. Registration of the twocoating patterns is achieved by maintaining the tool rollers 460, 474 ina precise angular relationship with one another, as will be describedhereinafter.

Referring to FIG. 5, a close-up view of a portion of first and secondpatterned rolls 560, 574 is illustrated. First patterned roll 560 has afirst pattern 562 for forming a microreplicated surface. Second patternroll 574 has a second microreplicated pattern 576.

In the example embodiment shown, first and second patterns 562, 576 arethe same pattern, though the patterns may be different. As a web 522passes over the first roll 560, a first curable liquid (not shown) on afirst surface 524 is cured by a curing light source 525 near a firstregion 526 on the first patterned roll 560. A first microreplicatedpatterned structure 590 is formed on the first side 524 of the web 522after the liquid is cured. The first patterned structure 590 is anegative of the pattern 562 on the first patterned roll 560. After thefirst patterned structure 590 is formed, a second curable liquid 581 isdispensed onto a second surface 527 of the web 522. To insure that thesecond liquid 581 is not cured prematurely, the second liquid 581 isisolated from the first curing light 525, typically by a locating thefirst curing light 525 so that it does not fall on the second liquid581. Alternatively, shielding means 592 can be placed between the firstcuring light 525 and the second liquid 581. Also, the curing sources canbe located inside their respective patterned rolls where it isimpractical or difficult to cure through the web.

After the first patterned structure 590 is formed, the web 522 continuesalong the first roll 560 until it enters the gap region 575 between thefirst and second patterned rolls 560, 574. The second liquid 581 thenengages the second pattern 576 on the second patterned roll and isshaped into a second microreplicated structure, which is then cured by asecond curing light 535. As the web 522 passes into the gap 575 betweenfirst and second patterned rolls 560, 574, the first patternedstructured 590, which is by this time substantially cured and bonded tothe web 522, restrains the web 522 from slipping while the web 522begins moving into the gap 575 and around the second patterned roller574. This removes web stretching and slippages as a source ofregistration error between the first and second patterned structuresformed on the web.

By supporting the web 522 on the first patterned roll 560 while thesecond liquid 581 comes into contact with the second patterned roll 574,the degree of registration between the first and second microreplicatedstructures 590, 593 formed on opposite sides 524, 527 of the web 522becomes a function of controlling the positional relationship betweenthe surfaces of the first and second patterned rolls 560, 574. TheS-wrap of the web around the first and second patterned rolls 560, 574and between the gap 575 formed by the rolls minimizes effects oftension, web strain changes, temperature, microslip caused by mechanicsof nipping a web, and lateral position control. Typically, the S-wrapmaintains the web 522 in contact with each roll over a wrap angle of 180degrees, though the wrap angle can be more or less depending on theparticular requirements.

To increase the degree of registration between the patterns formed onopposite surfaces of a web, it preferred to have a low-frequency pitchvariation around the mean diameter of each roll. Typically, thepatterned rolls are of the same mean diameter, though this is notrequired. It is within the skill and knowledge of one having ordinaryskill in the art to select the proper roll for any particularapplication.

EXAMPLE #2 Apparatus for Making Two-Sided Microreplicated Article

Because the features sizes on the microreplicated structures on bothsurfaces of a web are desired to be within fine registration of oneanother, the patterned rolls need to be controlled with a high degree ofprecision. Cross-web registration within the limits described herein canbe accomplished by applying the techniques used in controllingmachine-direction registration, as described hereinafter. Control ofregistration in the machine direction is required, which heretofore hasnot been achieved in two-sided microreplicated webs. For example, toachieve about 10 microns end-to-end feature placement on a 10-inchcircumference patterned roller, each roller must be maintained within arotational accuracy of ±32 arc-seconds per revolution. Control ofregistration becomes more difficult as the speed the web travels throughthe system is increased.

Applicants have built and demonstrated a system having 10-inch circularpatterned rolls that can create a web having patterned features onopposite surfaces of the web that are registered to within 2.5 microns.Upon reading this disclosure and applying the principles taught herein,one of ordinary skill in the art will appreciate how to accomplish thedegree of registration for other microreplicated surfaces.

Referring to FIG. 8, a schematic of a motor arrangement 800 used inApplicants' system is illustrated. Motor arrangement includes a motor810 including a primary encoder 830 and a drive shaft 820. Drive shaft820 is coupled to a driven shaft 840 of patterned roll 860 through acoupling 825. A secondary, or load, encoder 850 is coupled to the drivenshaft 840. Using two encoders in the motor arrangement described allowsthe position of the patterned roll to be measured more accurately bylocating the measuring device (encoder) 850 near the patterned roll 860,thus reducing or eliminating effects of torque disturbances when themotor arrangement 800 is operating.

Referring to FIG. 9, a schematic of the motor arrangement of FIG. 8, isillustrated as attached to control components. In the example apparatusshown in FIGS. 1-3, a similar set-up would control each motorarrangement 210 and 220.

Motor arrangement 900 communicates with a control arrangement 965 toallow precision control of the patterned roll 960. Control arrangement965 includes a drive module 966 and a program module 975. The programmodule 975 communicates with the drive module 966 via a line 977, forexample, a SERCOS fiber network. The program module 975 is used to inputparameters, such as set points, to the drive module 966. Drive module966 receives input 480 volt, 3-phase power 915, rectifies it to DC, anddistributes it via a power connection 973 to control the motor 910.Motor encoder 912 feeds a position signal to control module 966. Thesecondary encoder 950 on the patterned roll 960 also feeds a positionsignal back to the drive module 966 via to line 971. The drive module966 uses the encoder signals to precisely position the patterned roll960. The control design to achieve the degree of registration isdescribed in detail below.

In the example embodiments shown, each patterned roll is controlled by adedicated control arrangement. Dedicated control arrangements cooperateto control the registration between first and second patterned rolls.Each drive module communicates with and controls its respective motorassembly.

Various options are available for co-coordinating the two axes such asmaster/slave-type and parallel configurations, which was used inApplicants' system.

The control arrangement in the system built and demonstrated byApplicants include the following. To drive each of the patterned rolls,a high performance, low cogging torque motor with a high-resolution sineencoder feedback (512 sine cycles×4096 drive interpolation>>2 millionparts per revolution) was used, model MHD090B-035-NG0-UN, available fromBosch-Rexroth (Indramat). Also the system included synchronous motors,model MHD090B-035-NG0-UN, available from Bosch-Rexroth (Indramat), butother types, such as induction motors could also be used. Each motor wasdirectly coupled (without gearbox or mechanical reduction) through anextremely stiff bellows coupling, model BK5-300, available from R/WCorporation. Alternate coupling designs could be used, but bellows stylegenerally combines stiffness while providing high rotational accuracy.Each coupling was sized so that a substantially larger coupling wasselected than what the typical manufacturers specifications wouldrecommend. Additionally, zero backlash collets or compressive stylelocking hubs between coupling and shafts are preferred. Each rollershaft was attached to an encoder through a hollow shaft load sideencoder, model RON255C, available from Heidenhain Corp., Schaumburg,Ill. Encoder selection should have the highest accuracy and resolutionpossible, typically greater than 32 arc-sec accuracy. Applicants'design, 18000 sine cycles per revolution were employed, which inconjunction with the 4096 bit resolution drive interpolation resulted inexcess of 50 million parts per revolution resolution giving a resolutionsubstantially higher than accuracy. The load side encoder had anaccuracy of +/−2 arc-sec; maximum deviation in the delivered units wasless than +/−1 arc-sec.

Preferably, each shaft is designed to be as large a diameter as possibleand as short as possible to maximize stiffness, resulting in the highestpossible resonant frequency. Precision alignment of all rotationalcomponents is desired to ensure minimum registration error due to thissource of registration error. One of ordinary skill in the art willrecognize that there are various ways to reduce registration error dueto alignment of the rotational components.

The control strategy for each axis is implemented as follows:

Referring to FIG. 11, in Applicants' system identical position referencecommands were presented to each axis simultaneously through a SERCOSfiber network at a 2 ms update rate. Each axis interpolates the positionreference with a cubic spline, at the position loop update rate of 250microsecond intervals. The interpolation method is not critical, as theconstant velocity results in a simple constant times time interval path.The resolution is critical to eliminate any round off or numericalrepresentation errors. Axis rollover must also be addressed. It iscritical that each axis' control cycle is synchronized at the currentloop execution rate (62 microsecond intervals).

The top path 1151 is the feed forward section of control. The controlstrategy includes a position loop 1110, a velocity loop 1120, and acurrent loop 1130. The position reference 1111 is differentiated, onceto generate the velocity feed forward terms 1152 and a second time togenerate the acceleration feed forward term 1155. The feed forward path1151 helps performance during line speed changes and dynamic correction.

The position command 1111 is subtracted from current position 1114,generating an error signal 1116. The error 1116 is applied to aproportional controller 1115, generating the velocity command reference1117. The velocity feedback 1167 is subtracted from the command 1117 togenerate the velocity error signal 1123, which is then applied to a PIDcontroller. The velocity feedback 1167 is generated by differentiatingthe motor encoder position signal 1126. Due to differentiation andnumerical resolution limits, a low pass Butterworth filter 1124 isapplied to remove high frequency noise components from the error signal1123. A narrow stop band (notch) filter 1129 is applied at the center ofthe motor-roller resonant frequency. This allows substantially highergains to be applied to the velocity controller 1120. Increasedresolution of the motor encoder also would improve performance. Theexact location of the filters in the control diagram is not critical;either the forward or reverse path are acceptable, although tuningparameters are dependent on the location.

A PID controller could also be used in the position loop, but theadditional phase lag of the integrator makes stabilization moredifficult. The current loop is a traditional PI controller; gains areestablished by the motor parameters. The highest bandwidth current looppossible will allow optimum performance. Also, minimum torque ripple isdesired.

Minimization of external disturbances is important to obtaining maximumregistration. This includes motor construction and current loopcommutation as previously discussed, but minimizing mechanicaldisturbances is also important. Examples include extremely smoothtension control in entering and exiting web span, uniform bearing andseal drag, minimizing tension upsets from web peel off from the roller,uniform rubber nip roller. In the current design, a third axis geared tothe tool rolls is provided as a pull roll to assist in removing thecured structure from the tool.

The web material can be any suitable material on which a microreplicatedpatterned structure can be created. Examples of web materials arepolyethylene terephthalate, polymethyl methacrylate, or polycarbonate.The web can also be multi-layered. Since the liquid is typically curedby a curing source on the side opposite that on which the patternedstructure is created, the web material must be at least partiallytranslucent to the curing source used. Examples of curing energy sourcesare infrared radiation, ultraviolet radiation, visible light radiation,microwave, or e-beam. One of ordinary skill in the art will appreciatethat other curing sources can be used, and selection of a particular webmaterial/curing source combination will depend on the particular article(having microreplicated structures in registration) to be created.

An alternative to curing the liquid through the web would be to use atwo part reactive cure, for example, an epoxy, which would be useful forwebs that are difficult to cure through, such as metal web or webshaving a metallic layer. Curing could be accomplished by in-line mixingof components or spraying catalyst on a portion of the patterned roll,which would cure the liquid to form the microreplicated structure whenthe coating and catalyst come into contact.

The liquid from which the microreplicated structures are created istypically a curable photopolymerizable material, such as acrylatescurable by UV light. One of ordinary skill in the art will appreciatethat other coating materials can be used, and selection of a materialwill depend on the particular characteristics desired for themicroreplicated structures. Similarly, the particular curing methodemployed is within the skill and knowledge of one of ordinary skill inthe art. Examples of curing methods are reactive curing, thermal curing,or radiation curing.

Examples of coating means that useful for delivering and controllingliquid to the web are, for example, die or knife coating, coupled withany suitable pump such as a syringe or peristaltic pump. One of ordinaryskill in the art will appreciate that other coating means can be used,and selection of a particular means will depend on the particularcharacteristics of the liquid to be delivered to the web.

Various modifications and alterations of the present invention will beapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not limited to the illustrative embodiments set forthherein.

1. A microreplicated article comprising: a flexible substrate havingfirst and second opposed surfaces; a first coated microreplicatedpattern on the first surface; and a second coated microreplicatedpattern on the second surface, wherein the first and second patterns areregistered to within 100 microns in a cross-web direction.
 2. Thearticle of claim 1, wherein the first microreplicated pattern includes aplurality of cylindrical lenses.
 3. The article of claim 2, wherein thesecond microreplicated pattern includes a plurality of symmetric prisms.4. The article of claim 3, wherein first and second microreplicatedpatterns cooperate to form a plurality of lenticular lenses.
 5. Thearticle of claim 4, wherein the lenses have a pitch of about 150 micronsin a cross-web direction.
 6. The article of claim 5, wherein thesubstrate material is polyethylene terephthalate.
 7. The article ofclaim 6, further including a first land area between the firstmicroreplicated pattern and the web and a second land area between thesecond microreplicated pattern and the web.
 8. The article of claim 7,wherein the first land area is at least about 10 microns.
 9. The articleof claim 8, wherein the second land area is at least about 25 microns.10. The article of claim 9, wherein the cylindrical lenses have aneffective diameter of about 142 microns and the symmetrical prisms havean included angle of about 60 degrees.
 11. A method of making amicroreplicated article including a web substrate having first andsecond opposed surfaces, the method comprising: passing the web througha casting apparatus; coating a first liquid on the first surface;contacting the first liquid with a first patterned roll; curing thefirst liquid to create the first microreplicated pattern; coating asecond liquid on the second surface; contacting the second liquid with asecond patterned roll while the first microreplicated pattern is incontact with the first pattern roll; and curing the second liquid tocreate the second microreplicated pattern, wherein the first and secondpatterns are registered to within about 100 microns in a cross-webdirection.
 12. The method of claim 11, wherein said passing a webincludes passing a web made of polyethylene terephthalate.
 13. Themethod of claim 11, wherein said contacting the first liquid includescontacting a light sensitive acrylate resin solution.
 14. The method ofclaim 12, wherein said contacting the second liquid includes contactinga light sensitive acrylate resin solution.
 15. The method of claim 11,wherein said step of contacting the first liquid with the firstpatterned roll further includes contacting the first liquid with thefirst patterned roll, wherein the first patterned roll includes aplurality of symmetrical arcuately-shaped features.
 16. The method ofclaim 11, wherein said step of contacting the second liquid with thesecond patterned roll further includes contacting the second liquid withthe second patterned roll, wherein the second patterned roll includes aplurality of symmetrical prism-shaped features.
 17. The method of claim16, further including forming a first land area between the web and thefirst microreplicated pattern.
 18. The method of claim 17, furtherincluding forming a second land area between the web and the secondmicroreplicated pattern.
 19. An article comprising a web having firstand second opposed surfaces, the web further having a firstmicroreplicated pattern on the first surface and a secondmicroreplicated pattern on the second surface, wherein the first andsecond microreplicated patterns cooperate to form a plurality oflenticular lens features, the article made by a method comprising:passing the web through a casting apparatus; coating a first liquid onthe first surface; contacting the first liquid with a first patternedroll; curing the first liquid to create the first microreplicatedpattern; coating a second liquid on the second surface; contacting thesecond liquid with a second patterned roll while the firstmicroreplicated pattern is in contact with the first pattern roll; andcuring the second liquid to create the second microreplicated pattern,wherein the first and second patterns are registered to within about 100microns.
 20. An method of making an article including a plurality ofmicroreplicated lens features, the method comprising: providing asubstrate, in web form, having first and second opposed surfaces;passing the substrate through a casting apparatus to form a plurality oflens features, wherein the lens features are comprised of: a firstmicroreplicated patterned structure on the first surface and a secondmicroreplicated patterned structure on the second surface, wherein thefirst and second structures are registered to within about 100 microns.21. The method of claim 20, wherein the lens features are lenticularlenses.